Re: how and why does FSH affect masculine fertility ?

FSH..follicle stimulating hormone, is synthesized by the anterior pituitary 
gland under the direction of GnRH from the hypothalamus.  FSH specifically 
targets the Sertoli cells of the testes.  The Sertoli cells are also called 
nurse cells because of their role in nourishing and protecting the 
developing sperm cells.  Without stimulation by FSH, Sertoli cells will not 
function properly.  They will not be able to support the developing 
spermatozoa and may even lose contact with cells such as the spermatogonia.  

Hormone replacement therapy with urofollitropin may be able to reverse the 
defect as long as the Sertoli cells have functional FSH receptor.  

ICSI, intra-cytoplasmic-sperm-injection, involves using micromanipulation 
to physically insert a sperm or even spermatid into the cytoplasm of an 
oocyte. This process can be used to fertilize oocytes with sperm that have 
poor or zero motility. Furthermore, sperm cells can be harvested directly 
from the testes using various techniques such as a biopsy, core sample of 
seminiferous tubules.  If the testes are subfunctional because of low or no 
FSH stimulation, even ICSI would likely have limited utility in providing 
fertility.

A couple of good sources of information on this topic is the Textbook of 
Medical Physiology, 10th ed. Guyton and Hall, Saunders Pub.  and Knobil and 
Neill, The Physiology of Reproduction 2nd ed. Raven Press.

David Mallory
Associate Professor
Department of Biological Sciences
Marshall University
Huntington, WV USA